1. Field of the Invention
This invention relates to the materials of members used in a vibration wave driving device.
2. Related Background Art
As the frictional materials of a vibration wave driving device, there have been proposed various combinations of the materials of a vibration member and a portion of contact with a contact member contacting with the vibration member, and for example, in a vibration wave motor as a vibration wave driving device described in Japanese Patent Application Laid-Open No. 5-211785, a combination of resin of the polyimide origin and alumina is proposed as the material of the contact surface of a moving member as the contact member contacting with the contact surface of the vibration member. This combination provides good performance regarding abrasion.
In the above-described example of the prior art, however, when the driving device was actually driven as a motor, there was a case where there was very rarely formed film called transfer film which was the phenomenon that depending on the load condition and the number of revolutions, the component of resin adhered to the surface of alumina of the partner member.
As long as this transfer film is uniformly formed, the disadvantage that the coefficient of friction is reduced and torque becomes small only occurs. That is, the pressure contact force between the frictional materials can be increased correspondingly to the small coefficient of friction.
In the example of the prior art, however, depending on the driving condition of the motor, the state of formation of the transfer film differs, and as the state of formation, there are various cases such as a case where the transfer film is thinly and uniformly formed on the whole surface, a case where the transfer film is not formed at all, and a case where the transfer film is thickly formed at some locations.
A fluctuation of the motor performance occurs due to the difference between these states of formation of the transfer film. Also, if the motor is left under high humidity conditions and thereafter is again left under low humidity conditions, resin and alumina will be secured to each other and a so-called mutual adherence of the frictional materials will occur. If the adherence occurs, the motor will not start, and even if it starts, resin will be partially peeled off and will adhere to the surface of alumina which is the partner material. Therefore, the state of contact of the frictional sliding portion will become unstable, causing an irregularity of rotation of the motor.